We are studying the distribution and function of germ line specific DNA sequences using the ciliated protozoan, Tetrahymena as a model system. We have constructed a partial library of germ line, micronuclear DNA in the plasmid vector pBR322. We have developed a method for rapid screening of these clones to Southern blots of micro-and macronuclear DNA. This method will be used to identify clones which are eliminated from the vegetative macronucleus. Nullisomic strains of Tetrahymena, that is strains lacking one or more of the five chromosome pairs in the micronucleus, have been provided by Peter Bruns (Cornell). Micronucleus-specific clones will be hybridized to Southern blots of restricted micronuclear DNA from nullisomic strains in order to map the DNA sequences to the Tetrahymena chromosomes. If transcription of germ line specific DNA occurs, it will probably be during conjugation. RNA will be isolated from synchronized conjugating cells and probed with micronucleus-specific clones in order to detect putative complementary transcripts.